Bump bond structure for enhanced electromigration performance

Abstract

A microelectronic device has a pillar connected to an external terminal by an intermetallic joint. Either the pillar or the external terminal, or both, include copper in direct contact with the intermetallic joint. The intermetallic joint includes at least 90 weight percent of at least one copper-tin intermetallic compound. The intermetallic joint is free of voids having a combined volume greater than 10 percent of a volume of the intermetallic joint; and free of a void having a volume greater than 5 percent of the volume of the intermetallic joint. The microelectronic device may be formed using solder which includes at least 93 weight percent tin, 0.5 weight percent to 5.0 weight percent silver, and 0.4 weight percent to 1.0 weight percent copper, to form a solder joint between the pillar and the external terminal, followed by thermal aging to convert the solder joint to the intermetallic joint.

What is claimed is: 
     
       1. A microelectronic device, comprising:
 a die having a terminal; 
 a copper-containing pillar electrically coupled to the terminal, the copper-containing pillar including at least 90 weight percent copper; and 
 an intermetallic joint on the copper-containing pillar, the intermetallic joint electrically coupling the copper pillar to an external terminal; 
 wherein:
 the intermetallic joint includes at least 90 weight percent of at least one copper-tin intermetallic compound (IMC) selected from the group consisting of Cu 6 Sn 5  and Cu 3 Sn, and includes 0.1 weight percent to 5 weight percent silver; 
 the intermetallic joint is free of voids having a combined volume greater than 10 percent of a volume of the intermetallic joint; and 
 the intermetallic joint is free of a void having a volume greater than 5 percent of the volume of the intermetallic joint. 
 
 
     
     
       2. The microelectronic device of  claim 1 , further including a dielectric material surrounding the intermetallic joint. 
     
     
       3. The microelectronic device of  claim 2 , wherein the dielectric material includes inorganic dielectric particles. 
     
     
       4. The microelectronic device of  claim 1 , wherein the intermetallic joint includes Cu 6 Sn 5  and Cu 3 Sn. 
     
     
       5. The microelectronic device of  claim 4 , wherein:
 the external terminal includes copper in direct contact with the intermetallic joint; and 
 more than half of the Cu 3 Sn is located within 2 microns of the copper-containing pillar or within 2 microns of the external terminal. 
 
     
     
       6. The microelectronic device of  claim 1 , wherein a thickness of the intermetallic joint between the copper-containing pillar and the external terminal is 20 percent to 40 percent of a height of the copper-containing pillar. 
     
     
       7. The microelectronic device of  claim 1 , wherein the intermetallic joint is free of a region of tin that is not alloyed with copper. 
     
     
       8. The microelectronic device of  claim 1 , wherein the microelectronic device is free of a barrier layer between the copper pillar and the intermetallic joint, the barrier layer including a metal selected from the group consisting of nickel, cobalt, tungsten, molybdenum, and an alloy containing nickel, cobalt, tungsten, or molybdenum. 
     
     
       9. A microelectronic device, comprising:
 a die having a terminal; 
 a pillar electrically coupled to the terminal; 
 an intermetallic joint on the pillar, the intermetallic joint electrically coupling the copper pillar to an external terminal, the external terminal including copper in direct contact with the intermetallic joint; 
 wherein:
 the intermetallic joint includes at least 90 weight percent of at least one copper-tin intermetallic compound (IMC) selected from the group consisting of Cu 6 Sn 5  and Cu 3 Sn, and includes 0.1 weight percent to 5 weight percent silver; 
 the intermetallic joint is free of voids having a combined volume greater than 10 percent of a volume of the intermetallic joint; and 
 the intermetallic joint is free of a void having a volume greater than 5 percent of the volume of the intermetallic joint. 
 
 
     
     
       10. The microelectronic device of  claim 9 , wherein a thickness of the intermetallic joint between the copper-containing pillar and the external terminal is 20 percent to 40 percent of a height of the copper-containing pillar. 
     
     
       11. The microelectronic device of  claim 9 , wherein the intermetallic joint is free of a region of tin that is not alloyed with copper. 
     
     
       12. The microelectronic device of  claim 9 , further including a barrier layer between the pillar and the intermetallic joint, the barrier layer including a metal selected from the group consisting of nickel, cobalt, tungsten, molybdenum, and an alloy containing nickel, cobalt, tungsten, or molybdenum.